The present invention relates to an electromagnetic interference-shielding, flame-retardant ABS resin composition which has a high retention of electromagnetic interference-shielding performance even when the composition is exposed to such a high temperature atmosphere as 50.degree. C. or higher or exposed to such an atmosphere that the temperature thereof is varied to cycle between 50.degree. C. or higher and 0.degree. C. or lower.
ABS resins are widely used in the so-called office automation field as materials for making electronic parts and housings. For these purposes, materials are required to have high degree flame retardance and flame-retardant ABS resins meeting the requirements of the UL standard 94 V-0 of U.S.A are used as a rule.
Additionally, it is indispensable to subject such electronic parts and housings to electromagnetic interference-shielding treatment as provided in the U.S. FCC regulation relating to the prevention of electromagnetic interference. It has been investigated as a method of the electromagnetic interference-shielding treatment that an electrically conductive filler such as metallic fibers, metallic foils, carbon fibers, or the like is blended into a resin or a special resin such as a flame-retardant ABS resin depending on the application purpose (e.g. Japanese Patent Application Laid-Open No. 150203/83 corresponding to GB 2112796A).
However, the blending of a conductive filler such as aluminum fibers, aluminum flakes, brass fibers and the like into a flame-retardant ABS resin has the drawback of deteriorating the flame-retardance though its cause is not clear, thus making it difficult to meet the requirements of the UL standard 94 V-0. In consequence, it is conceivable in this case to increase the mixing proportion of the flame retardant for the purpose of improving the deterioration of the flame retardance, but this method is not necessarily desirable since this will worsen physical properties and the appearance of the molded articles and increase the material cost.
On the other hand, it has been found that, although such a resin composition containing aluminum fibers or the like exhibits a high electromagnetic interference-shielding performance, this initial performance is markedly lowered when the composition is exposed, for instance, to a 50.degree. C. or higher temperature atmosphere or to such an atmosphere that the temperature thereof is varied to cycle between 50.degree. C. or higher and 0.degree. C. or lower (i.e. thermal shocks are given).
Electromagnetic interference-shielding resins used for electronic parts and housings as stated above are considered to be exposed to such variation in temperature environments as above during transportation by ship or aircraft or during service under some conditions. Accordingly, there has been requested early development of such a flame-retardant ABS resin composition that the flame retardance thereof is not deteriorated and the electromagnetic interference-shielding performance thereof does not vary.